688 PROFESSOR W. C. M‘INTOSH AND MR E, E. PRINCE ON 
globule passes in later stages under the embryo, and for some time moves freely; but 
about the fifth day, when the blastopore closes, it becomes fixed, generally at the point 
coinciding with the vegetal pole. It now exhibits a thick layer of protoplasm, which 
becomes vacuolated in a complex manner, and gives origin to numerous nuclear structures 
as well as pigment-spots (PI. XI. figs. 12, 13). In certain cases (gurnard) the peri- 
blast was observed to bend in from the blastodermic layers, and carry the oil-globule 
with it at its margin.* 
PERIVITELLINE SPACE. 
This space is generally very distinct, and contains a transparent fluid, usually said to be 
water, which enters the ovum after fertilisation. In an undetermined species the space 
is enormously enlarged (PI. XIII. fig. 3). RercHerr, however, very lately observed that 
under the action of nitric acid it exhibited whitish flakes (No. 134, p. 463), Ransom again 
states that when the funnel of the micropyle is withdrawn from the discus proligerus (in 
Gastrosteus), water enters “to fill the breathing chamber.” This view was questioned by 
one of us in a short paper read at the British Association in 1885 (No. 122), the following 
statement being made :—‘‘ That a certain amount of water finds access to this space is 
possible, but in stained sections the fluid filling the chamber often appears coagulated and 
faintly stained, thus indicating the presence of minute protoplasmic particles. 1t would 
appear to be, therefore, a dilute plasma.” Rarraxce has recently stated that the fluid 
is albuminous (No. 125a). In the gurnard various granular bodies, probably portions of 
protoplasm of a circular form, have been seen. It is possible that these agree with the 
segmenting corpuscles of RypER and the expulsive bodies of RarraEtz.t 
Ill. Exrruston AND DEPOSITION. 
The ova when ripe either pass directly into the body-cavity from the ovaries and out 
by an external pore, as in the Salmonidz and Anguilla, or they pass to the posterior end 
of the ovary as they become mature, and thence by an oviducal aperture to the exterior. 
The latter is the more prevalent mode, and it presents two types according as the act of 
deposition is very rapid, as in the Cottoids, Discoboli, and certain Blennies; or it is slower, 
as in the Gadide, and may be even prolonged, as appears to be the case with T’rigla. 
The difficulty of ascertaining the real facts in regard to oviposition is apparent when 
it is remembered that, about even so familiar a form as the salmon, opinion has been 
up till comparatively recent times divided; the fishermen being of opinion that the 
process is gradual, and may occupy many days, whereas there is much evidence to show 
that the ova are discharged all at once, or very rapidly. In stripping a ripe female the 
* J. A. Ryper (Amer. Nat., vol. xx. p. 987) states that the periblast is hypoblastic, and that the only source of 
the nuclei in the pigment-cells of the oil-drop must be periblast; therefore these cells are hypoblastic in origin. 
Kinosiry and Conn severally observe (op. cit., p. 188) that possibly the ova of all the Gadide have one or more 
conspicuous oil-globules in the deutoplasm. 
+ Op cit., p. 16. He also thinks the perivitelline space has a phylogenetic significance. 
